For engine systems in vehicular or other mobile applications where a supply of hydrogen is utilized, due to challenges related to on-board storage of a secondary fuel and the current absence of a hydrogen refueling infrastructure, hydrogen is preferably generated on-board using a fuel processor. The hydrogen-containing gas from the fuel processor can be used to regenerate, desulfate and/or heat engine exhaust after-treatment devices, can be used as a supplemental fuel for the engine, and/or can be used as a fuel for a secondary power source, for example, a fuel cell. In some applications the demand for the hydrogen-containing gas produced by the fuel processor is highly variable.
One type of fuel processor is a syngas generator (SGG) that can convert a fuel reactant into a gas stream containing hydrogen (H2) and carbon monoxide (CO), known as syngas. Air and/or a portion of the engine exhaust stream can be used as an oxidant reactant for the fuel conversion process. The exhaust stream typically contains oxygen (O2), water (H2O), carbon dioxide (CO2), nitrogen (N2) and sensible heat, which can be useful for the production of syngas. Steam and/or water can optionally be added. The fuel supplied to the SGG can conveniently be chosen to be the same hydrocarbon fuel that is used in the engine. Alternatively a different fuel can be used, although this would generally involve a separate secondary fuel source and supply system specifically for the SGG. The H2 and CO can be beneficial in processes used to regenerate exhaust after-treatment devices. For other applications, for example, use as a fuel in a fuel cell, the syngas stream can be additionally processed prior to use.
The thermochemical conversion of a hydrocarbon fuel to syngas is performed in a SGG at high operating temperatures with or without the presence of a suitable catalyst. Parameters including equivalence ratio (ER) and operating (reaction) temperature are typically adjusted in an attempt to increase the efficiency of the fuel conversion process while reducing the undesirable formation of carbon (coke or soot), which can cause undesirable effects within the SGG and/or in downstream components. The term equivalence ratio (ER) herein refers to a ratio between the actual amount of oxygen supplied and the theoretical stoichiometric amount of oxygen which would fully react with the fuel present in the reactant mixture supplied to the SGG. An ER of greater than 1 represents a fuel lean mode (excess oxygen), while an ER of less than 1 represents a fuel rich mode (excess fuel). The term carbon herein includes solid fraction particulates of elemental carbon including graphitic carbon, coke and soot. Over time, carbon accumulation can impede the flow of gases, increase the pressure drop across the SGG and its associated components, and reduce the operating life or durability of the SGG. Large accumulations of carbon also have the potential to create excessive amounts of heat that can damage the SGG if the carbon is converted (for example, combusted or oxidized) in a short period of time.
While many have attempted to eliminate or reduce carbon formation, practically there is always a tendency for carbon to form during the conversion of the fuel into syngas. A particulate filter, also known as a particulate trap, soot filter or soot trap, can be employed within, at least partially within, or downstream of a fuel processor to collect or trap carbon from the product syngas stream. This allows for increased control and management of the particulates. The particulate filter can be, for example, a wall-flow monolith, a fibrous structure, a foam structure, a mesh structure, an expanded metal type structure or a sintered metal type structure. The particulate filter can be constructed from a suitable material, for example, ceramic materials, and may or may not contain one or more catalysts. Typically, carbon can be allowed to collect until the accumulation begins to adversely affect the gas flow across the particulate filter. A subsequent carbon removal process can be initiated to remove the carbon particulates collected by the particulate filter. The term “carbon gasification” herein includes one or a combination of combustion, oxidation, gasification or other carbon conversion processes by which carbon is removed. Methods to gasify carbon can include, for example, operating the SGG, at least periodically, with an increased equivalence ratio in a fuel lean mode or in a fuel rich mode within a desired temperature range. The equivalence ratio can be increased, for example, by reducing the mass flow of the fuel supply, turning the fuel supply off for a period of time, pulsating the mass flow rate of the fuel supply between a reduced and normal operating flow, or increasing the mass flow of the oxidant supply. Carbon gasification can occur in either fuel lean or fuel rich modes. An alternative approach to gasify carbon is to increase the atomic oxygen-to-carbon (O/C) ratio by adding a supplemental oxygen-containing reactant, for example, water can be introduced into the SGG. The carbon gasification process can be used to regenerate the filter in situ from time to time, and then it will continue to trap carbon particulates.
Prior methods to initiate and/or cease the regeneration process of a particulate filter include methods based on parameters that are indicative of carbon accumulation in the particulate filter, for example, sensing a pressure differential across (upstream and downstream of) the particulate filter, sensing a change in pressure upstream of the particulate filter, sensing a change in electrical conductivity near or within the particulate filter. Other methods are based on empirical results, for example, performing regeneration during predetermined operating conditions and sensing the elapsed time since previous regeneration. In applications where the fuel processor is subjected to highly variable and transient operating conditions and/or is less predictable, it can be advantageous to employ a regeneration scheme based on parameters that are indicative amounts of carbon accumulation in the particulate filter.
In vehicular or other mobile applications, an on-board SGG should generally be low cost, compact, light-weight, of low power consumption, efficiently packaged with other components of the engine system, and be of high reliability and high durability. Disadvantages of employing sensing devices for initiating and optionally ceasing a regeneration process of a particulate filter of a fuel processor include:                (a) the increase in quantity of components and their associated potential failure mechanisms, including reduced reliability and/or durability due to potential contamination and/or blockage of sensors,        (b) the additional cost of sensors and associated hardware,        (c) the increase in size, weight and power requirements of the SGG.        
The present approach to improved carbon management control for a fuel processor is effective in reducing the requirement for sensing devices and addressing at least some of the issues discussed above, for fuel processors in engine system and other applications.